Process: In an age of collaborative discoveries, questions of fairness are raised. But it's part of the history of the prizes.

A few hours after he won a Nobel Prize Thursday, Dr. Peter Agre stepped up to a microphone at the Johns Hopkins School of Medicine and made a startling announcement to the audience of journalists and well-wishers: "I didn't do this work."

Agre said he didn't deserve all the credit for his path-breaking discovery of aquaporins, proteins that regulate the flow of water in all living cells. The real work, he stressed, was done by the young researchers in his laboratory who put in long hours each day. "I made the coffee and sharpened the pencils," he said.

Few of Agre's colleagues were conned by the Midwesterner's humility: Even the 54-year-old researcher's scientific rivals agree that he earned the honor. But Agre's remarks last week touched on a sore point among scientists about the Nobel: In an age when most breakthroughs emerge from the joint effort of dozens or more people over many years, who should get credit?

On the day that Agre spoke to reporters about winning the chemistry prize, a full-page ad appeared in The Washington Post claiming that the Nobel judges who awarded the medicine prize to two scientists for the development of magnetic resonance imaging had improperly excluded a pioneer in the field.

"The Nobel Committee has exhibited a wanton disregard for the truth," said Dr. Raymond Damadian, a Long Island physician and entrepreneur who has been credited with helping discover the imaging technology. He placed the $80,000 ad to lobby for Nobel recognition. "If I had never been born," he said, "MRI would not exist today."

Controversy and questions of fairness have swirled around the Nobel since Swedish dynamite inventor Alfred Nobel first established the awards. Nobel, who died from a stroke in 1896, wrote in his will that his $9 million estate was to endow five awards - physics, chemistry, medicine, literature and peace - to recognize people who "rendered the greatest service to mankind." (The prize for economics wasn't added until 1968.)

As specified in Nobel's will, the Royal Swedish Academy of Sciences in Stockholm would select the winners of the chemistry and physics prizes, while the Karolinska Institute chose the winner in medicine. Later rules limited the winners in any category to three individuals.

Thanks to international news coverage and a monetary award even then worth more than 30 times what a scientist typically earned, the Nobels rapidly grew in influence after the first were given out in 1901.

"The public and the scientific institutions bought into the cult of the prize very quickly," said Robert Marc Friedman, author of Politics of Excellence: Behind the Nobel Prize in Science, a 2002 history of the award.

By 1906, Cosmopolitan magazine declared: "The history of modern science might be written without going outside the names of the Nobel prizes."

As scholars would later discover when the Nobel Foundation in Stockholm partially opened its archives in 1974, the issue of credit has been an issue from the prize's earliest days.

Elisabeth Crawford, a sociologist and historian of science who studied how judges arrived at their decisions between 1901 and 1950, found that Marie Curie would not have shared the 1903 physics prize for the discovery of radioactivity if her husband, Pierre, hadn't refused to accept the award without her. Historians argue that the 1952 medicine prize for discovering the antibiotic streptomycin failed to include Albert Schatz, a graduate student working for the scientist who received the award.

And sometimes, the judges honored scientists whose contributions have been questionable. John J.R. Macleod, for example, was awarded the 1923 medicine prize with Frederick Banting for the discovery of insulin - though Macleod was on vacation when the discovery was made, Crawford said.

Maurice Wilkins, who shared the 1962 prize in medicine with James Watson and Francis Crick for the discovery of the structure of DNA, is now thought by some historians to have played less of a role than other scientists.

The judges haven't always identified the most worthy science. In the past, for example, the Nobel went to researchers who developed the lobotomy and the pesticide DDT, both now widely discredited. The Nobel vaults also reveal that some who perhaps deserved the prize never got it. Among the famous nominated losers: Thomas Edison, Sigmund Freud, the Wright brothers and astronomer George Hale, whose observations provided evidence for the expansion of the universe.

The most unlucky candidate, however, was Arnold Sommerfeld, a brilliant 20th-century German physicist who received 81 nominations over five decades. He was run over by a car in 1951.

Politics clearly plays a role. Crawford, for example, found that a stubborn judge held up Albert Einstein's Nobel for years because of a prejudice against theoretical physics. When Einstein finally won the physics prize in 1923, it wasn't for his groundbreaking relativity theory but his less earth-shaking law of the photoelectric effect.